RECENT WORK ON PROTEIN-HYDROLYSIS 433 



mixture of peptone solution and intestinal epithelium with sodic 

 chloride and acetic acid. The coagulum thus obtained was 

 filtered off, and the filtrate examined. It gave no biuret reaction, 

 but } r ielded a crystalline precipitate when a solution of phospho- 

 tungstic acid was added to it. The idea that the peptone 

 had been converted into coagulable proteid and so removed was 

 negatived by the discovery that the filtrate from the coagulum 

 contained nitrogen equal in amount to that of the original 

 peptone used. 



In subsequent experiments Cohnheim used an extract of the 

 epithelium instead of the mucous membrane itself. He ground 

 up with sand the lining of the intestine of various animals 

 killed during active digestion, extracted the mass with alkaline 

 normal saline solution, and pressed out the extract in an iron 

 tincture-press. On standing for some time a good deal of 

 coagulable proteid was deposited, which was filtered off, and 

 the filtrate employed in the same way as originally he had used 

 the intestinal epithelium itself. Such extracts were found to 

 possess the power of causing the disappearance of peptone. 



The experiments clearly pointed to the existence in the 

 intestinal mucous membrane of a new proteoclastic enzyme, 

 differing from those known up to the time of the experiments 

 in having no action on the coagulable proteids, such as albumins 

 and globulins, nor upon fibrin, but possessing the power of 

 decomposing proteoses and peptones, and forming from them 

 crystalline bodies which do not give the biuret reaction, and 

 which are thrown out of solution by the presence of phospho- 

 tungstic acid. 



It is evident that these observations throw some light upon 

 the uncertainty which has hitherto existed as to the digestive 

 value of the succus entericus. Very conflicting statements have 

 been made as to its power of acting on coagulable proteids in 

 liquids of different reactions. As the experiments with the juice 

 were mainly made on coagulable proteids and not on peptone 

 alone, the results could only be discordant. 



Cohnheim isolated the enzyme from his extracts by gradually 

 adding ammonium sulphate and separating fractionally. He 

 gave it the name erepsin. 



The enzyme was thrown out of solution when the extract 

 contained 60 per cent, of ammonium sulphate. In later pre- 

 parations of it Cohnheim mixed two volumes of the extract 



